1. Field of the Invention
The present invention relates to a structure of a power semiconductor device used for a power transistor module which may be applied to an inverter device, for example.
2. Description of the Related Art
A conventional power semiconductor device is constructed in a manner to have the assembly of a circuit containing the power chip, the drive circuit of the power chip, and the protective circuit of the power chip, mounted on a planar surface of a substrate, and a package covering the circuit assembly and the planar surface of the substrate.
FIG. 3 shows a conventional assembly structure for a power transistor module. In FIG. 3, a metal insulating plate 1 is constructed by forming copper foil conductive patterns 1c having a thickness of about several tens of micrometers on a metal plate 1a of aluminum. The metal plate 1a serves as a heat sink base through an insulating layer 1b such as epoxy resin. A power transistor chip 2 is mounted on the metal insulating plate 1, and various electronic parts 3, such as diode chips, form a control circuit. Bonding wires 4 connect each of the power chips 2 and the electronic parts 3 to the conductive patterns 1c. A package 5 covers the device, and an outer lead terminal 6 extends outwardly, penetrating the package 5. The main circuit current, which flows to the power chip 2, is taken out through the conductive pattern 1c formed on the substrate and the outer lead terminal 6.
Since the conductive patterns 1c of the substrate 1 are used as a main circuit internal wiring connection as they stand in the above-mentioned structure, it is necessary that a path width of the copper foil conductive pattern 1c of the substrate 1 be enlarged so as to obtain a desired electrical capacitance. The path width must become larger as the electrical capacitance is increased. Consequently, the desired area of a metal insulating substrate is increased and the structure contained in the package 5 inevitably becomes larger, thereby leading to higher cost.